In this letter, we describe strong Bragg scattering induced by the PR effect in high-Q LN ring resonators measured at 1.8. Cryogenic operation of LN microring resonators is critical for the exploitation of the strong Pockels nonlinearity of LN for microwave-to-optical photon conversions[1]}, [2]}, [3]} and cryogenic-to-room-temperature data links[4]}. As the temperature decreases, the relaxation time of the PR effect increases from tens of milliseconds at room temperature [5]}, [6]} to several days at 1.8[7]}. Thus the PR effect induced electric field can semi-permanently modulate the refractive index of ring cavity. In particular, a periodic refractive index pattern similar to a Bragg-grating reflector can be built up when launching strong optical standing wave into selected modes of the cavity. Subsequently, when probed with a weak light, the microring exhibits mode splitting at phase matched wavelengths.An illustration of such a mechanism is shown in Fig. REF . A non-universal mode splitting of cavity resonances has been reported in optical resonator with fine lithographically engineered cavity [8]}. Here we achieved selective mode splitting with all-optical control. Moreover, by strongly exciting other cavity modes, the imprinted index pattern could be redistributed, thus reconfigure the mode splitting to other wavelengths. These interesting observations suggest potential exploitation of PR effect for on-chip all-optically controlled photonic components.
